CVE-2026-5163 json
Missing authorization check in AI message rewrite endpoint allows access to private thread content
published 5mo ago modified 28d ago also GHSA-8r89-8w26-cq32 , GO-2026-5263 , EUVD-2026-30753
- cvss
- 6.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 10%
- public exploits
- 0
- none known
Summary
Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645
Patch / fix
- go github.com/mattermost/mattermost/server/v8 8.0.0-20260401090745-f4d1abe7e8f5, 11.5.2
- go github.com/mattermost/mattermost-server 5.3.2-0.20260401090745-f4d1abe7e8f5, 11.5.2+incompatible
- Mattermost Mattermost 11.5.2, 11.6.0
- govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
opensuse advisories openSUSE-SU-2026:21483-1
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Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 5mo ago
Exploit prediction
0.21% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |
| GitHub | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost/server/v8 | >=11.5.0, <11.5.2 <8.0.0-20260401090745-f4d1abe7e8f5 |
11.5.2 8.0.0-20260401090745-f4d1abe7e8f5 |
| go | github.com/mattermost/mattermost-server | <5.3.2-0.20260401090745-f4d1abe7e8f5 >=11.5.0+incompatible, <11.5.2+incompatible |
5.3.2-0.20260401090745-f4d1abe7e8f5 11.5.2+incompatible |
| go | github.com/mattermost/mattermost-server/v5 | all versions |
no fix listed |
| go | github.com/mattermost/mattermost-server/v6 | all versions |
no fix listed |
Affected products
- Mattermost Mattermost
Classification
- Weakness
-
- CWE-862 Missing Authorization
References
Sources
- CVE List CVE-2026-5163
- GitHub Advisory GHSA-8r89-8w26-cq32
- NVD CVE-2026-5163
- OSV GO-2026-5263
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